Background
The present invention relates to a run-flat tire, which is capable of running for some time even after the tire has become uninflated or flat.
The run-flat tire is the kind of tire that has a wall-rigidity capable of bearing the load of the vehicle until reaching the nearest service station even when the pneumatic pressure of the tire becomes insufficient or zero due to a puncture or other causes.
Various kinds of structures have been proposed for such run-flat tires. A typical run-flat tire is disclosed in JP-A-62 279107(1987) for example. This tire has a side-reinforcing rubber pad which is crescent in vertical section (a section including the tire axis) and which is attached to the inner surface of a carcass layer extending from near the upper end of a rim flange to one end of a belt layer thereby reinforcing the side wall of the tire. This side-reinforcing rubber pad which is also called a lunette gives a "self supporting capability" to an flat tire and is usually formed of a rubber layer of high rigidity.
In the tire disclosed in EP 385192A1 (1990, counterpart of JP-A-02 283508), a single fibrous layer 103 formed of a fibrous cord ply extends from one side of the tire to the opposite side of the tire, that is, from one rim-fitting portion to another rim-fitting portion at opposite end. The fibrous layer 103 is inserted into a side-reinforcing rubber pad 102 along the center of the thickness of the rubber pad 102 as shown in FIG. 6. Such fibrous layer 103 is adapted to rigidify the side-reinforcing rubber pad so that when the tire gets punctured, generation of a crack in the side-reinforcing rubber pad resulting from an excessive compressive deformation is prevented.
Further, in the structure of the tire disclosed JP-A-05310013(1993), the fibrous layer 103 is arranged on the interface between an inner liner 105 and the side-reinforcing rubber pad 102 so that the fibrous layer 103 wraps up the inner surface of the side-reinforcing rubber pad 102 as shown in FIG. 7. Thus, it is described in the specification that with such structure, the durability life (a distance for which the tire is capable of running under a rated load, hereinafter referred to as the run-flat durability) of the tire in the flat condition can be increased.
However, since the fibrous layer which is strong against a tensile force is arranged on the inner surface of the tire subject to a compressive deformation, the effect of improving the durability of the tire has not been sufficient.
Further, inview of the rigidity of the side-reinforcing rubber pad due to the provision of the fibrous layer, the ride quality or ride comfortableness becomes worse.
In addition, in order to give the tire a sufficient degree of rigidity and durability, it has been necessary for the side-reinforcing rubber pad and the fibrous layer to have sufficiently large sizes which results in increasing the weight of the tire.